Awk and discarding non-matching tokens in a string?

Question

I'm having trouble getting a string tool to provide what I need (due to my ignorance). I have a string based on CPU features. The string will change as different processors offer different features:

# Example from a modern Core i5 4th gen
SUNCC_CXXFLAGS="-D__SSE2__ -D__SSE3__ -D__SSSE3__ -D__SSE4_1__ -D__SSE4_2__ -D__AES__ -D__PCLMUL__ __AVX__ ..."

The string works great for Sun Studio 12.3 and above. For Sun Studio 12.2 and below, I can only use SSE2, SSE3, SSSE3, SSE4.1 and SSE4.2. AES and above defines cause an obscure error, so they must be filtered out of the flags.

Put another way I need the intersection of the two sets:

# Cannot use AES and above for SunCC 12.2
ALLOWED_CXXFLAGS="-D__SSE2__ -D__SSE3__ -D__SSSE3__ -D__SSE4_1__ -D__SSE4_2__"
# New processor, needs to be filtered due to old compiler
SUNCC_CXXFLAGS="-D__SSE2__ -D__SSE3__ -D__SSSE3__ -D__SSE4_1__ -D__SSE4_2__ -D__AES__ -D__PCLMUL__ __AVX__ ..."

I've seen a number of questions and answers with awk matching (and non-matching) regexes and lines. But I need to filter based on tokens in a single line.

I tried the following, which does not produce expected results:

$ echo "-D__SSE2__ -D__SSE3__ -D__SSSE3__ -D__SSE4_1__ -D__SSE4_2__ -D__AES__ -D__PCLMUL__" | \
  nawk '!/(-D__SSE2__|-D__SSE3__|-D__SSSE3__)/'
$

Another twist: this is Solaris, so the tools don't have a lot of the options present in GNU tools. Its one of the reasons I tried awk instead of sed or grep.

How can I filter out the tokens that don't match my set of tokens?

Answer 1

To select only the SSE flags, try:

awk '/SSE/' ORS=' ' RS=' '

The key thing here is setting the record separators on input and output to a space. That way, each option is accepted or rejected separately.

For example:

$ SUNCC_CXXFLAGS="-D__SSE2__ -D__SSE3__ -D__SSSE3__ -D__SSE4_1__ -D__SSE4_2__ -D__AES__ -D__PCLMUL__ ..."
$ newFLAGS="$(echo "$SUNCC_CXXFLAGS" | awk '/SSE/' ORS=' ' RS=' ')"
$ echo "$newFLAGS"
-D__SSE2__ -D__SSE3__ -D__SSSE3__ -D__SSE4_1__ -D__SSE4_2__ 

SSE appears to be a tight enough match here. If it isn't, we can be more specific:

$ newFLAGS="$(echo "$SUNCC_CXXFLAGS" | awk '/^-D__(SSE2|SSE3|SSSE3|SSE4.1|SSE4.2)__/' ORS=' ' RS=' ')"
$ echo "$newFLAGS"
-D__SSE2__ -D__SSE3__ -D__SSSE3__ -D__SSE4_1__ -D__SSE4_2__ 

Alternative: excluding SSE and AES

$ echo "$SUNCC_CXXFLAGS" | nawk '!/SSE|AES/' ORS=' ' RS=' '
-D__PCLMUL__ ...

Keeping options that match SSE or sse

$ SUNCC_CXXFLAGS="-D__SSE2__ -D__SSE3__ -D__SSSE3__ -D__SSE4_1__ -D__SSE4_2__ -D__AES__ -D__PCLMUL__ -xarch=sse3"
$ newFLAGS="$(echo "$SUNCC_CXXFLAGS" | awk '/SSE|sse/' ORS=' ' RS=' ')"
$ echo "$newFLAGS"
-D__SSE2__ -D__SSE3__ -D__SSSE3__ -D__SSE4_1__ -D__SSE4_2__ -xarch=sse3

The change here is that we replaced the regex /SSE/ with /SSE|sse/. Because the vertical bar, |, means logical-or, this matches either SSE or sse.